Hydrorefining feed stock preparation

ABSTRACT

Pretreatment of a hydrorefining feed stock is effected in a fractionation or distillation facility having a plurality of separation zones. The feed stock is depentanized to remove cyclopentadiene and lower-boiling hydrocarbons; the bottoms, containing cyclopentadiene dimer, is rerun to reject high boiling material as a bottoms, and cyclopentadiene, from the conversion of the cyclopentadiene dimer, as overhead.

United States Patent 1191 Asselin 1 Aug. 28, 1973 [54] HYDROREFINING FEED STOCK 2,813,134 11/1957 Johnson et a1 203/29 PREPARA'HON 3,215,618 11/1965 Watkins 208/143 3,133,013 5/1964 Watk1ns.... 208/210 Inventor: George n, Mount Prospect. 3,161,586 12/1964 Watkins... 208/264 Ill. v 3,537,982 11/1970 Parker 208/255 [73] Assignee: Universal on Products Company, 3,457,163 7/1969 Parker 208/255 Des Plaines, 111. Primary Examiner-Delbert E. Gantz Flledl 1970 Assistant Examiner-Juanita M. Nelson [21] Appl' NOJ 100,104 Attorney-James R. Hoatson, Jr. and Robert W.

Erickson [52] US. Cl 208/255, 260/6815, 260/666 A,

203/28 [57] ABSTRACT [51] Int.Cl ..Cl0g 17/00 Pretreatment ofahydmrefining feed smckis effected [58] Field of Search 208/255; 203/28, in a fractionation or distillation facim havin a nab 203/29- 260/6815 666 A y g P 1ty of separanon zones. The feed stock 18 depentanlzed to remove cyc1opentadiene and 1ower-boi1ing hydro- [56] References Cited carbons; the bottoms, containing cyclopentadiene di- UNITED STATES PATENTS mer, is rerun to reject high boiling material as a bot- 2,51 1,936 6/1950 Morrell e1 al.. 260/666 A toms, and cyclopentadiene, from the conversion of the 2,397,580 4/1946 ward 260/666 cyclopentadiene dimer, as overhead, 3,557,239 1/1.971 Gebhart, Jr. et a1..... 260/6815 2,867,670 l/l959 McLean et a1 203/28 4 Claims, 1 Drawing Figure Depentanizer Charge Slack Hydroraf/ner Charge Ran/n Column Heavy fiarloms 1 HYDROREFINING FEED STOCK PREPARATION APPLICABILITY OF INVENTION The present invention involves the preparation of a hydrocarbonaceous feed stock. More specifically, my invention is directed toward a method of preparing a feed stock which is to be processed in a hydrorefining system. As utilized herein, the terms hydrorefining and hydrogenation" are intended to be synonymous and connote a process wherein various impurities are removed from a hydrocarbonaceous charge stock prior to subjecting the same to subsequent processing. Hydrorefining is generally practiced with respect to those charge stocks resulting from diverse conversion processes including the catalytic and/or thermal cracking of petroleum, often referred to as pyrolysis, shale oil retorting, the destructive distillation of wood or coal, etc. The distillate fractions from the normally liquid products of the foregoing processes, frequently contain impurities which necessarily must be removed before the fractions are suitable for their intended use. Such impurities include sulfurous compounds, nitrogenous compounds and oxygenated compounds, all of which cause the hydrocarbon distillate to exhibit corrosive tendencies, to be foul-smelling and to adversely affect the end use as petrochemicals, i.e., aromatics recovered by solvent extraction.

In addition to the aforementioned contaminating influences, or impurities, the hydrocarbon distillates contain appreciable quantities of unsaturated hydrocarbons including mono-olefinic, di-olefinic (including conjugated di-olefins) and aromatic hydrocarbons. The mono-olefinic and di-olefinic hydrocarbons induce the coke-forming characteristics of the hydrocarbon distillate, as do the styrenes, and, when subjected to hydrorefining for the purpose of removing the contaminating influences, difficulty is encountered due to the formation of coke and other carbonaceous materials. With respect to the coke formed as a result of the polymerization and co-polymerization tendencies of the olefinic hydrocarbons, perhaps the two most deleterious substances are cyclopentadiene and the styrenes.

Many hydrorefining processes have been designed to treat such hydrocarbon distillates successfully while simultaneously seeking to avoid many of the difficulties associated therewith. In general, these processes are effected in multiple-stage reaction systems functioning at various temperature levels. The desired end result is an aromatic-rich product stream from which the aromatic hydrocarbons may be easily recovered, for example, by way of solvent extraction. Typical of a two-stage process is that disclosed in U.S. Pat. No. 3,215,618 (Cl. 208-143 Two different three-stage systems are shown in U.S. Pat. Nos. 3,133,013 (Cl. 208-210) and 3, l 6] ,586 (Cl..l08-264). The charge stocks to such hydrorefining processes are generally not introduced directly into the reaction zone system. In as-received" condition, for example, a pyrolysis naphtha co-product will contain cyclopentadiene, and will. form polymerized products such as gums, during storage. This requires depentanization to reject the cyclopentadiene, followed by re-running to reject gums and other heavy polymers. Notwithstanding these precautions, as well as various process designs and techniques, polymer formation takes place, particularly in the first reaction zone, with the result that relatively frequent catalyst regeneration becomes necessary. This continued polymer formation-stems fromthe fact that cyclopentadiene dimer is formed in the depentanizer, or exists preformed in the as-received condition, and enters the rerun column as part of the depentanized bottoms feed. As the conditions required within the rerun column to separate the styrenes and the heavy polymers formed upon storage, the dimer is converted into cyclopentadiene which is removed as an overhead fraction with the feed to the hydrorefining reaction zone.

OBJECTS AND EMBODIMENTS An object of my invention is to prepare a hydrorefining feed stock substantially free from cyclopentadiene.

Another object of the present invention resides in improving the activity and stability of a catalyst employed in a process for hydrorefining coke-forming hydrocarbon distillates.

In one embodiment, therefore, my invention affords a method for preparing a hydrorefining feed stock substantially free from cyclopentadiene, which method comprises the steps of: (a) separating a charge stock containing monoand diolefinic hydrocarbons, including cyclopentadiene, in a first separation zone, to provide (i) a first hydrocarbon stream containing cyclopentadiene and (ii) a second hydrocarbon stream containing cyclopentadiene dimer; and, (b) separating said second hydrocarbon stream, in a second separation zone to provide (i) said feed stock and (ii) a third hydrocarbon stream containing cyclopentadiene resulting from the conversion of said cyclopentadiene dimer; said method further characterized in that said feed stock is withdrawn from said second separation zone through a locus above that into which said second bydrocarbon stream is introduced.

Other objects and embodiments of my invention invention involve preferred separation conditions and preferred processing techniques. One such processing technique involves introducing the third hydrocarbon stream into said first separation zone in order to reject the cyclopentadiene and recover aromatic hydrocarbons.

SUMMARY OF INVENTION The present inventive concept is founded on recognition of the fact that cyclopentadiene dimer is formed in the depentanizer at the conditions required to reject cyclopentadiene as an overhead fraction, or pre-exists in "as-received charge. The dimer is removed with the heavier bottoms, and is converted into cyclopentadiene in the rerun column at conditions which are required to reject styrenes and other heavy materials. Thus, with respect to the subsequent hydrorefining reaction system, one of the more deleterious substances in regard to catalyst activity and stability continues to remain in the pretreated charge stock. Through the utilization of the present invention, the method of pretreating the charge stock results in a hydrorefining feed material substantially from cyclopentadiene. The use of the term substantially free" is intended to connote a normally liquid, aromatic-rich feed stock containing less than about 0.05 percent by weight of cyclopentadiene.

The charge stock is originally introduced into a depentanizing column for the purpose of rejecting cyclopentadiene and low-boiling hydrocarbons as an overhead fraction, while retaining a hexane-plus material as the bottoms fraction period. Typically depentanizing conditions include a reboiler temperature in the range of about 250 F. to about 300 F., a top temperature of about 150 F. to about 200 F. and a top pressure in the range of about 20 psig. to about 40 psig., with a reflux ratio of about 0.5 to about 1.0, based on column charge. The operating conditions are adjusted in accordance with the characteristics of the charge stock in order to reject the cyclopentadiene as aforesaid. The bottoms fraction is introduced into a rerun column for the purpose of separating that desired fraction which is intended to be processed in the hydrorefining reaction system. Such a fraction is commonly limited to those normally liquid hydrocarbons containing from about six to about eight carbon atoms per molecule. Heretofore, the common practice has been to take the desired fraction as overhead from the rerun column while rejecting styrenes and heavier material as a bottoms fraction. At the conditions required to perform its intended function, the cyclopentadiene dimer, which was formed in the depentanizer, or preexisted, is converted into cyclopentadiene which then appears in the overhead fraction intended for hydrorefining.

In accordance with the present invention, the desired heart-cut is withdrawn from a locus above that through which the depentanized feed is introduced, with the result that the overhead is rich in cyclopentadiene, the desired fraction is substantially free from cyclopentadiene and the bottoms contains styrene and other heavier materials. The rerun column conditions include a bottom temperature in the range of about 350 F. to about 400 F., a top temperature of about 200 F. to about 250 F., a top pressure of about psig. to about psig. and a reflux ratio of about 0.5 to about 1.0, based on column charge. Under these conditions, the overhead from the rerun column will contain substantially all of the cyclopentadiene formed as a result of the conversion of the cyclopentadiene dimer. Since the overhead fraction will also contain a minor quantity of the desired aromatic-rich heart-cut, this fraction is, in a preferred embodiment, introduced into the depentanizer along with the fresh feed charge stock, whereby the cyclopentadiene is rejected in the overhead.

DESCRIPTION OF DRAWING In further describing the present method for preparing a hydrorefining feed stock, reference will be made to the accompanying drawing which is presented for the sole purpose of illustrating a preferred embodiment. In the drawing, the embodiment is presented by way of a simplified flow diagram in which such details as pumps, instrumentation and controls, heat-exchange and heat-recovery circuits, valving, start-up lines and similar hardware have been eliminated as non-essential to an understanding of the techniques involved. The use of such miscellaneous appurtenances, to modify the process as illustrated, will be evident to those possessing the requisite expertise in the petroleum refining art.

In the illustration, the charge stock is a raw pyrolysis gasoline having a gravity of about 509 API, a bromine number of about 106 and a diene value of about 103, and containing 1,000 ppm. by weight of sulfur present as sulfurous compounds. The desired end result is to recover an aromatic-rich naphtha fraction, containing C through C hydrocarbons substantially free from sulfurous compounds and olefinic hydrocarbons. These limitations are required since it is further intended that the aromatic-rich product will be ultimately subjected to a solvent extraction technique in order to recover LII benzene, toluene and mixed xylenes. Component analysis of the raw pyrolysis naphtha fraction are presented in the following Table I:

TABLE 1: Raw Pyrolysis Naphtha Fraction Component 1,3 Butadiene Butenes Butanes lso-pentane N-pentane Pentenes Pentadienes Cyclopentene cyclopentadiene C-6 PON C-7 PON Benzene Toluene Xylenes Heavier Parafl'lns, olefins and naphthenes The charge stock is introduced by way of line 1, admixed with a cyclopentadiene-rich recycle stream in line 2, the source of which is hereinafter described, and the mixture continues through line 1 into depentanizer 3. Depentanizer 3 functions at a bottom temperature of about 270 F., a top temperature of about 170 F. and a top pressure of about 25 psig. A cyclopentadiene and lighter overhead fraction, containing a minor quantity of C, hydrocarbons, is removed by way of line 4, cooled to a temperature of about F. in condenser 5, and introduced into reflux surge drum 6. A sufficient quantity is employed as reflux in line 7 in order to provide a reflux ratio of about 0.6, based on column feed, the remainder being withdrawn from the process through line 8.

The bottom stream in line 9, containing hexanes and heavier hydrocarbons including the cyclopentadiene dimer, is withdrawn by way of line 9 and introduced into rerun column 10 which functions at a bottom temperature of about 380 F. a top temperature of about 220 F and a pressure of about 0 psig. An overhead fraction containing cyclopentadiene resulting from the conversion of the cyclopentadiene dimer and about two percent by weight of the desired C, through C aromatic hydrocarbons, is withdrawn by way of line 1 l, cooled to a temperature of about 110 F. and introduced into reflux surge drum 13. A sufficient quantity of the overhead fraction is withdrawn as reflux in line 14 to provide a reflux ratio of about 0.6 based on column feed, the remainder, in order to recover the aromatics therein, is recycled by way of line 2 to combine with the charge stock in line 1 for introduction into depentanizer 3. The desired aromatic concentrate is withdrawn from rerun column 10 through line 15 at a locus above line 9 through which the depentanized feed is introduced. The heavier bottoms are withdrawn from the process by way of line 16. The component analysis of the hydrorefining feed stock withdrawn from line 15 is presented in the following Table II:

TABLE II: I-Iydroreflning Feedstock Component Wt.% C-6 PON 4.1 C-7 PON 25.3 Benzene 15.5 Toluene 10.7 Xylenes 5.9 Heavier 0.0

Analyses further indicate that the cyclopentadiene content of the hydroreflning feed stock is about 0.035

percent. A similar operation, conducted according to prior art practices, when the hydrorefining feed stock is the overhead fraction from the rerun column, the cyclopentadiene content is about one to two percent by weight and severely affects the hydrorefining catalyst.

I claim as my invention:

1. A method for preparing a hydro-refining feed stock substantially free from cyclopentadiene which comprises the steps of:

a. separating a charge stock containing monoand di-olefinic hydrocarbons, including cyclopenta' diene, in a first fractionation zone, to provide (1') a first hydrocarbon stream containing, cyclopentadiene and (ii) a second hydrocarbon stream containing cyclopentadiene dimer;

b. separating said second hydrocarbon stream, in a second fractionation zone, at a temperature range of between 200 F and 400 F, (i) said hydrorefining feed stock, substantially free from cyclopentadiene produced by the conversion of said cyclopentadiene dimer, and a third stream containing cyclo- I pentadiene, said method further characterized in that said hydrorefining feed stock is withdrawn from said second fractionation zone from a locus above that through which said second hydrocarbon stream is introduced; and,

0. recycling said third hydrocarbon stream to said first separation zone.

2. The process of claim 1 further characterized in that said feed stock comprises aromatics having six to eight carbon atoms per molecule.

3. The process of claim 1 further characterized in that said charge stock is a pyrolysis naphtha.

4. The method of claim 1 further characterized in that said charge stock is separated, in said first fractionation zone, at a reboiler temperature of about 250 F. to about 300 F. and a top pressure from about 20 psig to about 40 psig and said second hydrocarbon stream is separated, in said second fractionation zone, at a reboiler temperature of about 350 F. to about 400 F.

and a top pressure from 0 psig to about 15 psig. 

2. The process of claim 1 further characterized in that said feed stock comprises aromatics having six to eight carbon atoms per molecule.
 3. The process of claim 1 further characterized in that said charge stock is a pyrolysis naphtha.
 4. The method of claim 1 further characterized in that said charge stock is separated, in said first fractionation zone, at a reboiler temperature of about 250* F. to about 300* F. and a top pressure from about 20 psig to about 40 psig and said second hydrocarbon stream is separated, in said second fractionation zone, at a reboiler temperature of about 350* F. to about 400* F. and a top pressure from 0 psig to about 15 psig. 